Field of the Invention
The present invention relates to an image pickup apparatus, such as a digital camera, an electronic apparatus, and a method of calculating a light amount change characteristic of light from a photographing object.
Description of the Related Art
In recent years, image pickup apparatuses, such as a digital camera, have come to be equipped with an image pickup device improved in sensitivity. This has made it possible to photograph a picture without blurring at a high shutter speed even under a relatively dark environment, such as indoors. However, fluorescent lamps, which are widely used as indoor light sources, produce a phenomenon called flicker in which illumination light periodically fluctuates due to influence of the frequency of a power supply (in general, a commercial power supply). When image pickup is performed at high shutter speed under such a light source that produces flicker (hereinafter referred to as the “flickering light source”), exposure unevenness or color temperature variation of an image can be caused between frames due to the influence of flickering, and further, exposure unevenness and/or color unevenness sometimes occur(s) within one frame.
Further, image pickup apparatuses have become prevalent which are equipped with a live view function for sequentially displaying images periodically picked up by an image pickup device on a display section provided in the image pickup apparatus. Also in the live view function, in a case where the charge accumulation time period of each picked-up frame is short, exposure unevenness sometimes is caused within a frame due to the influence of flickering.
To solve this problem, in Japanese Patent Laid-Open Publication No. 2006-222935, there has been proposed a technique for detecting a state of flicker of illumination light, and adjusting the timing of image pickup such that the center of an exposure time substantially coincides with timing in which the light amount of the illumination light becomes a maximum value. Further, in Japanese Patent Laid-Open Publication No. 2006-222935, there has been proposed a technique for detecting an illuminance of the illumination light at sampling intervals of 1 msec, and detecting a blinking period of the illumination light based on a result of the detection of the illuminance.
However, in the method of detecting a state of flicker of illumination light, described in Japanese Patent Laid-Open Publication No. 2006-222935, the charge accumulation time period of a photoelectric conversion device used for the detection is limited. This causes a problem that under a condition of dark environmental light, erroneous detection of flicker is likely to occur. Further, also in a case where luminance variation is caused by a photographing object appearing in a photographing image, erroneous detection of flicker is likely to occur.